Published by Utah State University Extension and Utah Plant Pest Diagnostic Laboratory
ENT-164-12PR
June 2012
Beneficials: Predatory Mites
Ron Patterson, Carbon Co. Extension • Ricardo Ramirez, Extension Entomology Specialist
What you should know
• Predatory mites feed on all life stages of many
small arthropods and target pest spider mites.
• Most predatory mite species do best in humid
conditions and controlled environments such as
greenhouses and high tunnels, although some
species such as the western predatory mite tolerate high temperatures and low humidity.
• Predatory mites are commercially available to fit
most farm, landscape and garden situations.
• Predatory mites do not damage plants, but feed
on plant pollen when prey is unavailable.
P
redatory mites can provide natural pest control by
eating unwanted pests. These beneficial mites are
one way to maintain pest populations at non-damaging
levels, known as biological control. By encouraging
predatory mite populations, plants can be protected
from excessive pest attack and damage.
Mites are arthropods, characterized by having an exoskeleton and jointed appendages among other traits,
and are not insects. They belong to the same class as
spiders, Arachnida. There are over 40,000 recognized
species of mites worldwide. The most familiar are the pest
mites that feed on plants, such as the two-spotted spider
mite, an economically important pest of many crops.
There are also many predatory mites that feed on pest
mites and small insects.
Predatory mites occur naturally in varied habitats from
agricultural fields to small backyard gardens. It is best
to encourage native populations through recognized
conservation practices. These practices include scouting
for pests and predators and using “soft” pesticides rather
than broad-spectrum chemicals. Many beneficial species can also be purchased and released. It is crucial to
choose the mite species appropriate for the environment.
Most beneficial mites prefer higher humidity and lower
temperatures than what is common during the summer in
Utah. The most common commercially available beneficial species are shown in Table 1 (pg. 3).
Fig. 1. Western predatory mite (right) attacking a European red mite (left).1
The predatory mite that may do best outdoors in Utah is
the western predatory mite (Galendromus occidentalis).
Suppliers may use other names for the western predatory
mite, such as, Typhlodromus occidentalis or Mesoseiulus
occidentalis.
DESCRIPTION
Western predatory mites are very small (about 0.5 mm or
1/50 inch), typically requiring at least a hand lens to see
them. The adults are teardrop- or pear-shaped arachnids with four pairs of legs. They do not have antennae,
segmented bodies, or wings. Using a microscope, the
piercing-sucking mouthparts can be seen sticking out in
front of the head. Western predatory mites are smaller
or equal in size to most spider mite species. They are also
much more active than the slow moving pest mites. Their
bodies vary in color from cream to green to red, depending on the color of their recent food source.
Life cycle:
Predatory mites have five stages in their life cycle—egg,
six-legged larval stage, protonymph, deutonymph, and
adult. Most beneficial species have a life cycle very similar to what is outlined below.
Eggs are oval, clear, larger than spider mite eggs (which
are round), and typically laid on the underside of leaves.
They are laid individually and the larvae hatch in 2-3
days.
Larvae have three pairs of legs (six total) and begin-
feeding on prey immediately after hatching. After feeding on one or two prey for one or two days they molt to
the protonymph stage.
control agent. The additional food resource and limited
mobility allows predatory mites to act as “body guards”
and protect plants from pest mite outbreaks even when
pest populations are low.
Protonymphs and deutonymphs are first and sec-
ond stage nymphs, respectively, that increase in size and
have four pairs of legs (eight total). Each stage consumes
prey over one or two days, getting slightly larger and
eventually molting to adulthood.
Fig. 2. Female western predatory mite and eggs (white).2
Adult females consume about two prey per day for
about five to six weeks. They deposit an average of 33
eggs during that time. Males consume about one prey
per day for about four to five weeks.
Predatory mites have multiple generations per year and
develop from egg to adult in 6 – 12 days. Western predatory mites go into diapause (dormancy) when there
are less than 11 hours of daylight. There are, however,
non-diapausing strains that can be used effectively in
greenhouses during short winter days. Adults overwinter in
protected places, such as bark, leaves or soil debris.
Foraging:
Western predatory mites are quite versatile in that they
can be used in low-growing crops such as strawberries,
mid-height crops such as grapes and cane fruit, and tree
fruit crops. They will attack adult, juvenile, and egg stages
of many pests, such as two-spotted spider mites, McDaniel spider mites, yellow spider mites, apple and pear
rust mites, Prunus rust mites, blister mites, and sometimes
European red mites, making them a fairly versatile generalist predator. They will also feed on other predatory mites
and small insects. They consume their prey by piercing
and sucking them dry. Amblyseius spp. also tend to be
generalist while Neoseiulus cucumeris target thrips, and P.
persimilis targets spider mites more specifically.
Many predatory mites supplement their diet with plant
pollen, which helps limit their dispersal in the general
area where they are resident or released as a biological
UPPDL, 5305 Old Main Hill, Logan UT 84322, utahpests.usu.edu
PROMOTING BENEFICIAL MITES
Augmentation and Inoculation:
Predatory mites can be purchased through commercial
suppliers and they also occur naturally. Augmentation is
the practice of timing the introduction of a fresh population of predators to help the current native population
keep up with an observed or anticipated flare-up of a
pest population. Inoculation is the practice of introducing predators into an area where the population is low or
non-existent.
When pest spider mite populations are high it is better
to apply a “soft” pesticide, such as insecticidal soap or
horticultural oil, before introducing predators. This should
knock the pest mite population down so the predator
introduction can be more effective. If a miticide is to be
used in a “hot spot” it should be applied before the introduction of the predators—preferably several days before
the release. This strategy will improve the effectiveness of
the predatory mites. Read the pesticide label to select
the product that will best fit the pest management plan.
It is important to note that some pesticide-tolerant strains
of predatory mites are available as biological control
agents.
Release process:
Several species of predatory mites can be purchased
through commercial suppliers (Table 1, pg. 3). Select
the predatory mite that best fits the pest management
plan (e.g., target pest, greenhouse, etc.). Mites are usually shipped overnight in an insulated container with an
ice pack to improve survivability. When the shipment is
received it should be opened and inspected as soon as
possible to determine whether the mites are still alive.
The mites are typically combined with a carrier material, such as vermiculite, corncob dust, or sawdust. A light
spray of water on the application area will help the mites
and carrier material stay in place when they are applied
to the infested area. It is best to apply them to the field,
garden, or greenhouse as soon as possible to ensure their
survival. To avoid extreme heat
or cold that can decrease predator success, apply them in the
early morning or late evening.
Be sure to follow the supplier’s
instructions.
Fig. 3. Predatory mites are applied from a shaker container
provided by the commercial
supplier.3
T: 435.797.2435 F: 435.797.8197
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Depending on the predatory species and the pest mite
population level, recommendations are for a release of
2000 – 5000 predators per acre. If there are noted “hot
spots” of pests it is good to make sure the predators are
applied in those areas to help get those hot spots under
control.
Predator releases are more successful if early scouting
has detected pests before the population gets too high.
Begin in spring and check plants weekly for pest and
predatory mites. This will require at least a hand lens and
a lot of practice.
Conservation:
Conservation involves practices that encourage native
predatory mite populations. Many pesticides are just
as, or more, harmful to predatory mites as they are to
pest insects and mites. In fact, some pesticides, such as
imidacloprid, carbaryl, and malathion, actually promote
spider mite growth and/or reproduction while reducing
the resident predatory mite population. Often, secondary
outbreaks of pest mites result from the mortality of predatory mites following broad-spectrum pesticide applications for control of primary pests. Predatory mites can be
conserved by eliminating or reducing pesticides that are
toxic to arthropod predators.
Predatory mite adults become active in the spring before
the spider mite population emerges. Predators are most
likely to become established in perennial flowers, shrubs
and trees. The pollen, small insects and cool-season pest
mites in a perennial planting will help maintain a population that is ready to go to work when the pest populations
begin to increase. These perennial plantings would be
most effective as a border crop or as intercropped strips
within the crop area. A diverse habitat of plants will help
maintain a healthy beneficial mite population.
Selected References:
Alston, D. G., & Reding, M. E. (1997). Web Spinning Spider
Mites. Utah State University Cooperative Extension: http://
extension.usu.edu/files/publications/publication/webspinning-spider-mite97.pdf
Anonymous. Predator Mites Acari: Physoseiidae Typhlodromus spp. Amblyseius spp.: http://mint.ippc.orst.edu/
predmitefact.pdf
Ellis, B. W., & Bradley, F. M. (Eds.). (1996). The Organic Gardener’s Handbook of Natural Insect and Disease Control.
Emmaus, PA: Rodale.
Flint, M. L., & S. H. Dreistadt. (1998). Natural Enemies
Handbook: The Illustrated Guide to Biological Pest Control. Los Angeles: University of California Press.
Henn, T., Weinzierl, R., & Koehler, P. G. (2009). Beneficial
Insects and Mites. University of Florida IFAS Extension:
http://edis.ifas.ufl.edu/in078
Hoyt, S. C., & Beers, E. H. (1993). Western predatory mite.
Washington State University: http://jenny.tfrec.wsu.edu/
opm/displaySpecies.php?pn=830
Table 1. Many species of predatory mite are available to purchase. When making a purchase or researching which to use
to get the best success, take note of the pest species they attack, preferred plant environment, and optimal temperature
and humidity the mite species prefer.
Predatory mite species
Pest targeted
Phytoseiulus persimilis
Two-spotted spider mite Low growing plants
(strawberries), greenhouse plants
59 – 86°F
At least 60% RH
Galendromus occidentalis
(aka Typhlodromus or Mesoseiulus occidentalis)
Spider mites, eriophyid
mites, and others but
not red mite eggs
Tree fruits, cane fruits,
low-growing fruits,
corn, cotton
60 – 120°F
Tolerates low humidity, not below 30% RH.
Higher temps require
higher RH
Mesoseiulus longipes
Spider mites
Greenhouse plants
70 – 100°F
At least 40% RH at
70°F
Neoseiulus californicus
Spider mites, Willamete
mite, others
Roses, vegetables,
strawberries, corn
55 – 105°F
Prefers humid, tolerates down to 40% RH
Amblyseius fallacis
Two spotted spider
mite, European red
mite, spruce mite, pacific mite, others
Strawberries, peppers, raspberries,
mint, greenhouse
plants
48 – 85°F
At least 50% RH
Images courtesy of Elizabeth Beers, Washington State University
Image courtesy of Taunton Press, www.finegardening.com
Host plant
application
Optimal
Optimal relative
temperature humidity (RH)
1,2
3
Precautionary Statement: Utah State University Extension and its employees are not responsible for the use, misuse, or damage caused by application or misapplication of products or
information mentioned in this document. All pesticides are labeled with active ingredients, directions for use, and hazards, and not all are registered for edible crops. “Restricted use”
pesticides may only be applied by a licensed applicator. The pesticide applicator is legally responsible for proper use. USU makes no endorsement of the products listed herein.
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Noelle E. Cockett, Vice President for Extension and Agriculture, Utah State University.
Fact Sheet Series: Beneficial Insects
UPPDL, 5305 Old Main Hill, Logan UT 84322, utahpests.usu.edu
T: 435.797.2435 F: 435.797.8197
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